1. Field of the Invention
This application relates to inducing, promoting, or enhancing the growth, proliferation, regeneration, or survival of inner ear tissue, particularly inner ear epithelial hair cells. In addition, this application provides methods, compositions and devices for prophylactic and therapeutic treatment of inner ear disorders and conditions, particularly hearing impairments. The methods comprise administration of insulin-like growth factor-I (IGF-1) and/or fibroblast growth factor-2 (FGF-2), or their agonists.
2. Description of Related Disclosures
Hearing impairments are serious handicaps which affect millions of people. Hearing impairments can be attributed to a wide variety of causes, including infections, mechanical injury, loud sounds, aging, and chemical-induced ototoxicity that damages neurons and/or hair cells of the peripheral auditory system. The peripheral auditory system consists of auditory receptors, hair cells in the organ of Corti, and primary auditory neurons, the spiral ganglion neurons in the cochlea. Spiral ganglion neurons (xe2x80x9cSGNxe2x80x9d) are primary afferent auditory neurons that deliver signals from the peripheral auditory receptors, the hair cells in the organ of Corti, to the brain through the cochlear nerve. The eighth nerve connects the primary auditory neurons in the spiral ganglia to the brain stem. The eight nerve also connects vestibular ganglion neurons (xe2x80x9cVGNxe2x80x9d), which are primary afferent sensory neurons responsible for balance and which deliver signals from the utricle, saccule and ampullae of the inner ear to the brain, to the brainstem. Destruction of primary afferent neurons in the spiral ganglia has been attributed as a major cause of hearing impairments. Damage to the peripheral auditory system is responsible for a majority of hearing deficits (Dublin, 1976; Rybak, 1986; Lim, 1986; Pryor, 1994).
Hearing loss or impairment is a common occurrence for mammals. Impairment anywhere along the auditory pathway from the external auditory canal to the central nervous system may result in hearing loss. Auditory apparatus can be divided into the external and middle ear, inner ear and auditory nerve and central auditory pathways. While having some variations from species to species, the general characterization is common for all mammals. Auditory stimuli are mechanically transmitted through the external auditory canal, tympanic membrane, and ossicular chain to the inner ear. The middle ear and mastoid process are normally filled with air. Disorders of the external and middle ear usually produce a conductive hearing loss by interfering with this mechanical transmission. Common causes of a conductive hearing loss include obstruction of the external auditory canal, as can be caused by aural atresia or cerumen; thickening or perforation of the tympanic membrane, as can be caused by trauma or infection; fixation or resorption of the components of the ossicular chain; and obstruction of the Eustachian tube, resulting in a fluid-filled middle-ear space. Auditory information is transduced from a mechanical signal to a neurally conducted electrical impulse by the action of neuro-epithelial cells (hair cells) and SGN in the inner ear. All central fibers of SGN form synapses in the cochlear nucleus of the pontine brain stem. The auditory projections from the cochlear nucleus are bilateral, with major nuclei located in the inferior colliculus, medial geniculate body of the thalamus, and auditory cortex of the temporal lobe. The number of neurons involved in hearing increases dramatically from the cochlea to the auditory brain stem and the auditory cortex. All auditory informnation is transduced by a limited number of hair cells, of which the so-called inner hair cells, numbering a comparative few, are critically important, since they form synapses with approximately 90 percent of the primary auditory neurons. By comparison, at the level of the cochlear nucleus, the number of neural elements involved is measured in the hundreds of thousands. Thus, damage to a relatively few cells in the auditory periphery can lead to substantial hearing loss. Hence, many causes of sensorineural loss can be ascribed to lesions in the inner ear. This hearing loss can be progressive. In addition, the hearing becomes significantly less acute because of changes in the anatomy of the ear as the animal ages.
During embryogenesis, the vestibular ganglion, spiral ganglion, and the otic vesicle are derived from the same neurogenic ectoderm, the otic placode. The vestibular and auditory systems thus share many characteristics including peripheral neuronal innervations of hair cells and central projections to the brainstem nuclei. Both of these systems are sensitive to ototoxins that include therapeutic drugs, antineoplastic agents, contaminants in foods or medicines, and environmental and industrial pollutants. Ototoxic drugs include the widely used chemotherapeutic agent cisplatin and its analogs (Fleischman et al., 1975; Stadnicki et al., 1975; Nakai et al., 1982; Berggren et al., 1990; Dublin, 1976; Hood and Berlin, 1986), commonly used aminoglycoside antibiotics, e.g. gentamicin, for the treatment of infections caused by Gram-negative bacteria, (Sera et al., 1987; Hinojosa and Lemer, 1987; Bareggi et al., 1990), quinine and its analogs, salicylate and its analogs, and loop-diuretics.
The toxic effects of these drugs on auditory cells and spiral ganglion neurons are often the limiting factor for their therapeutic usefulness. For example, antibacterial aminoglycosides such as gentamicins, streptomycins, kanamycins, tobramycins, and the like are known to have serious toxicity, particularly ototoxicity and nephrotoxicity, which reduce the usefulness of such antimicrobial agents (see Goodman and Gilman""s The Pharmacological Basis of Therapeutics, 6th ed., A. Goodman Gilman et al., eds; Macmillan Publishing Co., Inc., New York, pp. 1169-71 (1980) or most recent edition). Aminoglycoside antibiotics are generally utilized as broad spectrum antimicrobials effective against, for example, gram-positive, gram-negative and acid-fast bacteria. Susceptible microorganisms include Escherichia spp., Hemophilus spp., Listeria spp., Pseudomonas spp., Nocardia spp., Yersinia spp., Klebsiella spp., Enterobacter spp., Salmonella spp., Staphylococcus spp., Streptococcus spp., Mycobacteria spp., Shigella spp., and Serratia spp. Nonetheless, the aminoglycosides are used primarily to treat infections caused by gram-negative bacteria and, for instance, in combination with penicillins for the synergistic effects. As implied by the generic name for the family, all the aminoglycoside antibiotics contain aminosugars in glycosidic linkage. Otitis media is a term used to describe infections of the middle ear, which infections are very common, particularly in children. Typically antibiotics are systemically administered for infections of the middle ear, e.g., in a responsive or prophylactic manner. Systemic administration of antibiotics to combat middle ear infection generally results in a prolonged lag time to achieve therapeutic levels in the middle ear, and requires high irritial doses in order to achieve such levels. These drawbacks complicate the ability to obtain therapeutic levels and may preclude the use of some antibiotics altogether. Systemic administration is most often effective when the infection has reached advanced stages, but at this point permanent damage may already have been done to the middle and inner ear structure. Clearly, ototoxicity is a dose-limiting side-effect of antibiotic administration. For example, nearly 75% of patients given 2 grams of streptomycin daily for 60 to 120 days displayed some vestibular impairment, whereas at 1 gram per day, the incidence decreased to 25% (U.S. Pat. No. 5,059,591). Auditory impairment was observed: from 4 to 15% of patients receiving 1 gram per day for greater than 1 week develop measurable hearing loss, which slowly becomes worse and can lead to complete permanent deafness if treatment continues.
Ototoxicity is also a serious dose-limiting side-effect for cisplatin, a platinum coordination complex, that has proven effective on a variety of human cancers including testicular, ovarian, bladder, and head and neck cancer. Cisplatin damages auditory and vestibular systems (Fleischman et al., 1975; Stadnicki et al., 1975; Nakai et al., 1982; Carenza et al., 1986; Sera et al., 1987; Bareggi et al., 1990). Salicylates, such as aspirin, are the most commonly used therapeutic drugs for their anti-inflammatory, analgesic, anti-pyretic and anti-thrombotic effects. Unfortunately, they have ototoxic side effects. They often lead to tinnitus (xe2x80x9cringing in the earsxe2x80x9d) and temporary hearing loss (Myers and Bernstein, 1965). However, if the drug is used at high doses for a prolonged time, the hearing impairment can become persistent and irreversible, as reported clinically (Jarvis, 1966).
Accordingly, there exists a need for means to prevent, reduce or treat the incidence and/or severity of inner ear disorders and hearing impairments involving inner ear tissue, particularly inner ear hair cells, and optionally, the associated auditory nerves. Of particular interest are those conditions arising as an unwanted side-effect of ototoxic therapeutic drugs including cisplatin and its analogs, aminoglycoside antibiotics, salicylate and its analogs, or loop diuretics. In addition, there exists need for methods which will allow higher and thus more effective dosing with these ototoxicity-inducing pharmaceutical drugs, while concomitantly preventing or reducing ototoxic effects caused by these drugs. What is needed is a method that provides a safe, effective, and prolonged means for prophylactic or curative treatment of hearing impairments related to inner ear tissue damage, loss, or degeneration, particularly ototoxin-induced, and particularly involving inner ear hair cells. The present invention provides compositions and methods to achieve these goals and others as well.
The present invention is based in part on the discovery disclosed herein that the inner ear hair cells produced FGF-2 in vivo, that utricular epithelial cells expressed FGF receptor in vitro, and that administration of certain growth factors can stimulate the proliferation of inner hair cells. Among 30 growth factors examined, FGF-2 was the most potent mitogen. IGF-1 was also effective. Accordingly, it is an object of the invention to provide a means of inducing, promoting, or enhancing the growth, proliferation, regeneration, or survival of inner ear tissue, particularly inner ear epithelial hair cells, in vitro, ex vivo or in vitro. It is a further object of the invention to provide a method for treating a mammal to prevent, reduce, or treat the incidence of or severity of an inner ear hair cell-related hearing impairment or disorder (or balance impairment), particularly an ototoxin-induced or -inducible hearing impairment, by administering to a mammal in need of such treatment a prophylactically or therapeutically effective amount of FGF-2, IGF-1, their agonists, a functional fragment or derivative thereof, a chimeric growth factor comprising FGF-2 or IGF-1, a small molecule or antibody agonist thereof, or a combination of the foregoing. Optionally, a trkB or trkC agonist, preferably a neurotrophin, more preferably NT-4/5, NT-3, or BDNF, and most preferably NT4/5, or a functional fragment or derivative thereof, a chimeric neurotrophin, a pantropic neurotrophin, or a small molecule or antibody agonist thereof, is also administered in the case where auditory or vestibular neuronal damage is also present or suspected. According to the method of this invention a composition of the invention can be administered at a suitable interval(s) either prior to, subsequent to, or substantially concurrently with the administration of or exposure to hearing-impairment inducing inner ear tissue damage, preferably ototoxin-induced or -inducible hearing impairment.
Also provided are improved compositions and methods for treatments requiring administration of a pharmaceutical having an ototoxic, hearing-impairing side-effect, wherein the improvement includes administering (prophylactically or therapeutically) a therapeutically effective amount of FGF-2, IGF-1, their agonists, a functional fragment or derivative thereof, a chimeric growth factor comprising FGF-2 or IGF-1, a small molecule or antibody agonist thereof, or a combination of the foregoing, to treat or prevent the ototoxicity induced by the pharmaceutical. Accordingly, it is an object of the invention to provide an improved composition containing FGF-2, IGF-1, their agonists, or a combination thereof, in combination with an ototoxic, hearing-impairing pharmaceutical drug for administration to a mammal. Such combination compositions can further contain a pharmaceutically acceptable carrier. The pharmaceutical composition will have lower ototoxicity than the ototoxic pharmaceutical alone, and preferably, will have a higher dosage of the ototoxic, pharmaceutical than typically used. Examples of such improved compositions include cisplatin or other ototoxic neoplastic agent or an aminoglycoside antibiotic(s) in combination with FGF-2, IGF-1, their agonists, or a combination thereof. A trkB or trkC agonist is optionally formulated or administered therewith when neuronal damage is present, suspected, or expected.
Still further, the invention relates to the use in medicine of compositions of the invention in cases of bacterial infection. The present invention provides a solution to the art that has long sought a therapy and a medicament which can treat the ototoxic effects currently associated with certain antibiotics, and particularly with the more popular and commonly used aminoglycoside antibiotics without sacrificing the antimicrobial effectiveness of the aminoglycosides.
Still further, the invention relates to the use in medicine of compositions of the invention in cases of cancer. The present invention provides a solution to the art that has long sought a therapy and a medicament which can treat the ototoxic effects currently associated with certain chemotherapeutics, and particularly with the more popular and commonly used cisplatin chemotherapeutics without sacrificing the antineoplastic effectiveness of cisplatin or its analogs.
Still further, the invention relates to the use in medicine of compositions of the invention in cases where diuretics are needed. The present invention provides a solution to the art that has long sought a therapy and a medicament which can treat the ototoxic effects currently associated with certain diuretics, and particular with the more popular and commonly used loop-diuretics, without sacrificing their diuretic effectiveness.
Still further, the invention relates to the use in medicine of compositions of the invention in cases where quinine or quinine-like compounds are needed. The present invention provides a solution to the art that has long sought a therapy and a medicament which can treat the ototoxic effects currently associated with certain quinines without sacrificing their effectiveness.
Additional objects and features of the invention will be apparent to those skilled in the art from the following detailed description and appended claims when taken in conjunction with the figures.